Insulin-like growth factor 2 (IGF2) as a driving force of exponential expansion in neonatal thymus. Insulin-like growth factor 2 (IGF2) as a driving force of exponential expansion in neonatal thymus

Like all organs, the thymus grows in size and function rapidly during development, which comes to a halt after birth. However, the molecular mechanisms behind such a transition in the thymus remain obscure. Using single-cell RNA sequencing (scRNA-seq) of the murine thymic stroma, we identified that major transcriptomic changes occur in the endothelium and mesenchyme across the transition to homeostasis. Differentially expressed gene and intercellular network analyses of temporally resolved scRNA-seq data revealed fibroblast-derived insulin-like growth factor 2 (IGF2) as a candidate driving neonatal thymic expansion. We demonstrated IGF2 activity promotes a cortical TEC-specific proliferation and is tightly regulated at the thymic growth transition. Bulk RNA-seq of human thymi across the transition also revealed IGF2 to drive thymic expansion, suggesting an evolutionarily conserved role. Our study highlights the role of a fibroblast-derived IGF2 in promoting cTEC proliferation, resulting in early thymic expansion that is followed by down-regulation to establish homeostasis. Overall design: For our time-series single-cell RNA sequencing, we used 3 thymi per library. Our merged scRNAseq dataset contains 3-day-old (3 Foxn1+/+ males, 3 Foxn1lacZ/lacZ males, 2 Foxn1+/+ females, 2 Foxn1lacZ/lacZ females), 7-day-old (2 Foxn1+/+ males, 3 Foxn1lacZ/lacZ males), 14-day-old (2 Foxn1+/+ males, 2 Foxn1lacZ/lacZ males, 2 Foxn1+/+ females, 2 Foxn1lacZ/lacZ females). 30-day-old (2 Foxn1+/+ males, 3 Foxn1lacZ/lacZ males) datasets are available in a separate manuscript, Xiao*, Kang* et al. (2025). GSE264402.

与所有器官一致，胸腺在发育过程中体积与功能均快速增长，该进程于出生后终止。然而，胸腺发育至稳态这一转变背后的分子机制仍不明晰。本研究通过对小鼠胸腺基质开展单细胞RNA测序（single-cell RNA sequencing, scRNA-seq），发现在胸腺向稳态转变的全过程中，内皮细胞与间充质细胞存在显著的转录组变化。对时序性scRNA-seq数据开展差异表达基因与细胞间互作网络分析后，本研究鉴定出成纤维细胞来源的胰岛素样生长因子2（insulin-like growth factor 2, IGF2）可作为驱动新生胸腺扩张的候选调控因子。本研究证实，IGF2可特异性促进皮质胸腺上皮细胞（thymic epithelial cell, TEC）增殖，并在胸腺生长转变阶段受到严格调控。对不同发育阶段的人胸腺进行批量RNA测序（bulk RNA-seq）的结果同样显示，IGF2可驱动胸腺扩张，提示该调控作用在进化过程中具有保守性。本研究阐明了成纤维细胞来源的IGF2在促进皮质胸腺上皮细胞增殖中的关键作用：该因子介导早期胸腺扩张，随后其表达下调以维持胸腺稳态。
实验整体设计：本研究的时序单细胞RNA测序实验中，每个文库使用3个胸腺样本。整合后的scRNA-seq数据集涵盖以下发育阶段样本：出生后3日龄组（Foxn1+/+雄性3只、Foxn1lacZ/lacZ雄性3只、Foxn1+/+雌性2只、Foxn1lacZ/lacZ雌性2只）；出生后7日龄组（Foxn1+/+雄性2只、Foxn1lacZ/lacZ雄性3只）；出生后14日龄组（Foxn1+/+雄性2只、Foxn1lacZ/lacZ雄性2只、Foxn1+/+雌性2只、Foxn1lacZ/lacZ雌性2只）。出生后30日龄组样本（Foxn1+/+雄性2只、Foxn1lacZ/lacZ雄性3只）的数据集已发表于另一篇论文Xiao*、Kang*等（2025），登录号GSE264402。